1. Field of the Invention
The present invention relates to tactile displays for computer systems that can be used to present Braille characters and other information with movable tactile elements that can be touched by a human user. In particular, the present invention relates to a refreshable tactile display using one actuator protected from touching forces for moving tactile elements and separate actuators to lock the tactile elements in place.
2. Description of the Related Art
To make computer systems accessible to visually impaired users, a tactile display with multiple tactile elements that can be touched by a user serves many purposes. A tactile display with two positions for the tactile elements (raised and lowered) can be used to form Braille characters that can be scanned by a trained user more rapidly than a speech synthesizer can pronounce the same material. A tactile display with contiguous tactile elements that each can assume one of two positions can form raised ridges against a recessed background that can be used to present lines, curves and blocked areas of black and white graphics. A tactile display with contiguous tactile elements that can each assume multiple vertical positions can form variably raised ridges that can be used to present topographic information, such as the contours of a face or a relief map of a portion of the earth's surface.
Typically, the tactical elements are cylindrical pins that can be moved by actuators up or down in the dimension defined by a long axis of the pins. The properties of tactile displays are controlled by the properties of actuators that can convert electric signals controlled by a computer processor to mechanical movement of tactile elements sufficient to be felt a human user.
Experience with Braille displays shows a human can feel a pin displacement of 0.010 inches when the human applies a force of 20 grams to the pin, so this force should be opposed by the display; and the human can feel a pin displacement of 0.020 to 0.030 inches without an opposing force, such as if the pin moves under the human's touch. The specifications for Braille characters and common extensions to Braille specifications, define characters that each are made of up to eight dots in two columns of up to four dots, include dots with a height difference (z-dimension) of about 0.019 inches, in. (0.48 millimeters, mm), a dot diameter of about 0.057 in. (1.45 mm), a spacing between dot centers in the same character of about 0.092 in. (2.34 mm), and a separation between corresponding positions on adjacent Braille characters of about 0.245 in. (6.22 mm) for adjacent characters on the same line (x-dimension) and, for six dot Braille characters, about 0.400 inches (10.16 mm) for adjacent characters on different lines (y-dimension). Typical embossed paper Braille displays, which are not refreshable, present 25 lines of 40 six-dot Braille characters that are found acceptable presentations for scanning.
Using conventional commercial refreshable Braille displays, 25 lines of 40 characters are not achieved. Instead, a single line with up to 80 characters, but more typically only 40 characters, is commercially available. For example the Power Braille 80 Display by Blazie Engineering, and available from Freedom Scientific, presents a single line of 80 eight-dot Braille characters on a relatively large flat rectangular box; the unit is 24 inches long (x-dimension), 11.5 inches wide (y-dimension), 1.5 inches thick (z-dimension), weighs about ten pounds, and retails for about $10,000. A 40-character display from the same company is about half as long (only 14 inches), half as heavy (about five pounds) and costs about half, but is about the same width (13 inches) and thickness (1.5 inches) as the 80-character display.
The actuators used by many commercial systems, including the Power Braille 40 and Power Braille 80, employ piezoelectric bending elements. These actuators are favored because they are simpler to manufacture, more reliable in use, and consume less power than arrays of tiny electromagnetic coils acting on magnetized pins; however, these actuators require considerably more space than electromagnetic coils. A piezoelectric material changes shape when subjected to a large electric field. Piezoelectric bending elements curl when subjected to a strong electric field, but the deflection at the end of a beam of such material is a small percentage (often less than 1%) of the length of the beam. To achieve a deflection of 0.02 inches, on the order of a Braille dot height, from a material with a 0.2% deflection in an electric field, a beam about 10 inches long is utilized. This provides an important reason for the great width (11.5 to 13 inches) of the Power Braille displays. In alternative configurations, small mechanical levers can be used to amplify small deflections, but such approaches increase the complexity and cost of such devices.
A simple approach is to use an array of small electromagnetic coils with magnetized cores to displace the pins that serve as tactile elements. Sizes useful for multi-line displays are not achieved unless the size of each electromagnet is about one sixth the area allotted for each six-dot Braille character on a page (or one eighth the area allotted for each eight-dot extended Braille character).
This approach suffers from several disadvantages. One disadvantage is that such tiny electromagnets are expensive to manufacture and assemble in arrays, are unreliable, and are difficult to replace in the tight arrays needed for Braille characters.
Another disadvantage is that such electromagnets consume substantial power to move a pin a Braille character height and sustain the pin in the moved position against the forces applied by a human reader. For example, it is assumed that an electromagnet consumes 100 milliWatts to move and sustain a pin in a non-rest state (either raised or lowered). A display having 25 lines of 40 eight-dot characters includes 8000 pins, and would consume 800 Watts to move all the pins. A graphical or topographical display would have many more pins in the same area and consume considerably more power. For example, each six-dot Braille character is allotted an area about 0.4 inches by 0.25 inches in which there would be 40 contiguous pins of diameter 0.05 inches. This is five times the number of pins used in the example Braille display, and results in a power consumption of 4000 Watts. A typical residential electrical outlet supplies only about 1200 Watts. Thus an array of small electromagnets can exceed the power capacity of a residential electric outlet for graphical or topographical displays.
Another disadvantage is that electromagnets small enough to generate Braille characters are still not small enough to represent graphic and topographic information, in which pins about the size of Braille dots are contiguous. The electromagnet diameter would be constrained to be about 0.05 to 0.06 inches in diameter.
In another approach, the electromagnets are used to raise the pins, but the pins are then locked in place so that the electromagnets do not have to expend power to maintain a pin in a non-rest position. Such an approach reduces the power problems in Braille and graphical or topographical displays. However, the complexity and cost of the display is increased by the extra components required for the locking mechanism in addition to the cost and complexity of the tiny electromagnets.
Another approach forms Braille characters on a rotating rim of a fixed wheel. For each dot of the three or fours dots on each column of a Braille character, two inverted “T” shaped grooves are cut in the wheel at different radii from the axis of rotation, separated by the Braille dot height distance. Flanges are added to the pins used as tactile elements to hold the pins in place in one of the two grooves. An electromagnetic coil moves a magnetized rod at a non-rotating position on the wheel and moves pins to engage one of the grooves. If the flange on the pin engages the outer groove, the pin is extended beyond the rim; if the flange engages the inner groove, the pin is recessed in the rim. Holes in the rotating rim drag both extended and recessed pins one circuit around the wheel in the grooves. When the pins return to the fixed position of the electromagnetic coils, the pins are reset to one of the two groves for the Braille characters on the next line. A reader positioned away from the electromagnetic coils reads the Braille characters as they rotate with the rim past the reader.
A disadvantage of this approach is the great thickness of a display device that accommodates the diameter of the wheel. Another disadvantage is that a reader cannot skim several lines during the time of a single rotation by the rim. Another disadvantage is that the approach is not suitable for displaying graphical information, which would employ many more than the one row provided by this approach. Another disadvantage is that the approach is not suitable for displaying topographical information, which would employ many more than the two radial positions allowed by the two grooves for the tactile elements.
A smaller, lighter mechanism to generate each character would allow multiple-line Braille displays favored for scanning by human users. A mechanism to generate each character that is less complex and less costly to manufacture would allow affordable prices that foster more widespread use. In addition, smaller and lighter mechanism would allow better tactile graphic and topographic displays.
Based on the foregoing, there is a clear need for a smaller, less complex mechanism for generating Braille characters in a refreshable display for computers.
In addition, there is a clear need for a smaller, less complex refreshable tactile display that represents graphical or topographical information.
In addition, there is a need for a smaller, less complex mechanism for a refreshable tactile display that can represent Braille characters and also can represent graphical information or topographical information or both.
The approaches described in this section could be pursued, but are not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.